The present invention relates to a non-contact power transmission apparatus.
FIG. 8 schematically shows a non-contact power transmission apparatus that wirelessly transmits power from a first copper wire coil 51 to a second copper wire coil 52, which is separated from the first copper wire coil 51, by using resonance of an electromagnetic field. Such an apparatus is disclosed, for example, in NIKKEI ELECTRONICS published on Dec. 3, 2007, pages 117 to 128 and International Patent Publication No. WO/2007/008646, In FIG. 8, a magnetic field generated at a primary coil 54 connected to an AC power source 53 is enhanced by magnetic field resonance by the first and second copper wire coils 51, 52, so that electrical power is generated at a secondary coil 55 through electromagnetic induction of the enhanced magnetic field of the second copper wire coil 52. The generated power is then supplied to a load 56. It has been observed that a 60-watt electric lamp, as the load 56, can be lit when first and second copper wire coils 51, 52 having a diameter of 30 cm are separated by 2 m.
To efficiently supply the output power of the AC power source 53 to the load 56 using the non-contact power transmission apparatus, it is necessary to supply the output power of the AC power source 53 to the resonance system (the first and second copper wire coils 51, 52 and the primary and secondary coils 54, 55). However, the above cited documents only disclose summaries of non-contact power transmission apparatuses, but do not specifically show what should be done to obtain a non-contact power transmission apparatus that satisfies the requirements.
When the distance between the first copper wire coil 51 on the transmission side and the second copper wire coil 52 on the reception side and the impedance of the load 56 are constant, a resonance frequency of the resonance system suitable for the impedance of the load 56 is obtained in advance by experiments. An AC voltage having the obtained resonance frequency is supplied from the AC power source 53 to the primary coil 54. However, when the impedance of the load 56 is changed, the power of the AC power source 53 cannot be efficiently supplied to the load 56. In this description, the resonance frequency of the resonance system refers to the frequency at which the power transmission efficiency is maximized.